A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
ActiveCell.Offset(0, 3).Range("A1").Value = Application.WorksheetFunction.Sum(Range("D" & CStr(FirstRow) & ":D" & CStr(LastRow)))
or easier:
ActiveCell.Offset(0, 3).Value = Application.Sum(Range("D" & FirstRow & ":D" & LastRow))
edit: Ahh, almost simultaneous posting.